Recently, there are demands for further increasing the optical density and bleeding resistance of images recorded by ink jet recording. Recording media on which images are recorded, in particular, plain paper, have different degrees of ink permeability, and such difference affects the image characteristics. In particular, a recording medium having high ink permeability tends to reduce the optical density of a recorded image and also tends to reduce the bleeding resistance. In recent years, ink jet recording has become popular, and recorded images are required to simultaneously achieve the above-mentioned performances at high levels regardless of the type of the recording medium, i.e., even on recording media having high permeability.
As countermeasures against the above, there are proposals focusing on the functional group of self-dispersible pigment (see PTLs 1 to 3). PTL 1 describes an ink containing self-dispersible pigment to a particle of which a functional group showing high reactivity to calcium is bonded and self-dispersible pigment to a particle of which a functional group different from the above-mentioned group is bonded. Such an ink can record an image with a high optical density. PTL 2 describes an ink containing self-dispersible pigment to a particle of which an ionic group is directly bonded and self-dispersible pigment to a particle of which an ionic group is bonded via another atomic group. Such an ink can reduce the dependency of the optical density on the type of plain paper. PTL 3 describes an ink containing self-dispersible pigment to a particle of which two types of functional groups are bonded. Such an ink can suppress a reduction in the optical density of a recorded image.